This application focuses on understanding the interaction between the E2F transcription factors and their critical upstream regulator, the retinoblastoma protein tumor suppressor. The Lees lab has constructed an E2f3 mutant mouse strain and shown that this member of the E2F family plays a critical role in controlling the transcription of most E2F-responsive genes and thereby the rate of cellular proliferation. The generation of compound mutant mice has been used to establish the role of E2F3 in tumorigenesis. Significantly this has yielded a mutant mouse strain that developed metastases at high frequency. Since metastasis is a rare event in mice, this represents an excellent model system in which to study this process. This application focuses on understanding the role of E2F3 in the regulation of proliferation, tumorigenesis and metastasis. It will involve the analysis of single and compound mutant mouse strains, chimeric animals and isolated cell lines. Microarray analysis of the E2f3 mutant cell lines will be used to conduct a genome-wide screen for genes that are regulated by E2F and play a critical role in the control of cellular proliferation. Mutant mouse strains and chimeras will be analyzed to determine the role of E2F3 in normal development, tumorigenesis and the suppression of metastasis. The analysis of paired primary and tumor cell lines from the metastatic mouse model will establish the molecular and cellular changes that trigger/accompany the process of invasion and metastasis. Finally, high throughput microarray-based genotyping will be used to map strain-specific modifiers of the E2f3 mutant phenotypes.